Basal Age

Basal age represents the highest level, on a test standardized in units corresponding to mental age or age-equivalents, below which it can be assumed that all items would be answered correctly. For example, a child who correctly answers the required number of items at a certain age level would be given credit for all preceding items on the test even though the child has not actually been tested on those items. The term basal age is often used interchangeably with basal score or basal.

The point at which to begin the calculation of basal age is usually estimated from a child's chronological age or, for children with learning or language disabilities, from a functional estimate of age. For children who demonstrate considerable scatter in their performance or who perform at significantly different levels from their age-matched peers, the calculation of a basal age makes it easier to determine a meaningful starting point on a test.

Although tests vary somewhat in how basal scores are calculated, the procedure is usually very similar. The Stanford-Binet Intelligence Scales (fifth edition), for example, uses basal levels in all its 11 testing blocks. Testing is begun at a block that is believed to represent a child's general ability level. If a basal is not obtained, testing moves back to successively lower blocks until a basal is established. On the Peabody Picture Vocabulary Test (third edition), a basal is established when a respondent makes no or only one error within a set of items. On the Woodcock Language Proficiency Battery-Revised, the number of correct responses required to establish a basal age varies between four and six, depending on the particular subtest.

On almost all tests, the examiner administers test items in reverse order from the estimated starting point until a basal is obtained in the manner specified. In the event that no basal level is achieved, the first item on the test is usually considered to represent the basal age.

Tests that employ basal scores typically also use ceiling scores, or previously defined accuracy levels that determine the point at which a test is terminated. Thus, the basal and ceiling essentially define an examinee's functional range. Moreover, they serve to limit the number of test items that are administered. Usually, age-equivalent scores are calculated based on the raw score derived from the ceiling item and the number of correct responses below it.